1. Field of the Invention
The present invention relates to a circuit for synchronizing a transmitting-receiving station to a data network of a digital communications system, comprising a correlation receiver in the receiving device comprising a transit time chain in which the input digital signal, a data block containing code words inserted at determinate points of the block (Barker code), is delayed, and further comprising of a number, corresponding to the number of signals, of parallel outputs of the transit time chain, each of which is connected to an inverter which can be set up in accordance with the Barker code and whose outputs are connected to a majority decision device which supplies a correlation signal which serves for synchronization purposes.
2. Description of the Prior Art
Digital communications systems transmit data flows between transmitting and receiving stations. In a data network, a whole series of receiving stations are connected to a single transmitting station. The connection can be established via a permanent wire line or by a radio channel. If further receiving stations are to be connected, before they are able to actively participate in the data exchange, they must be synchronized from an asynchronous state to the data network.
Depending upon the nature of the data transfer, various types of synchronization are needed for the synchronization process. Therefore, the receiving pulse train which follows the input signal is required for error-free recognition and processing of the received data. In dependence upon the characteristics of the transmission link, the received signal not only suffers weakening of level, but also transmit distortions or interference disturbances as a result of multi-channel propagation. The bit synchronization which is required in this case is achieved if the interrogation edge of the receiving pulse train comes to lie on the analog received signal at a time of approximately maximum read-out security.
If a data transmission is effected in a block-structured form, when the transmitting-receiving station is brought into synchronization, block synchronization is required in addition to bit synchronization.
For the determination of the block and phase relationship, special code words are transmitted at determinate positions in the block (Barker code) and are analyzed at the receiving end by auto-correlation techniques.
In synchronous networks, a fixed block relationship prevails between all of the transmitting/receiving stations to an approximate extent, i.e. except for radio transit time differences within a radio range. Bit synchronism is necessary for the stations directly participating with one another in the data exchange. Furthermore, the stations can operate with multiple access in which case the block-wise data exchange is always linked to fixed time locations. Therefore, each transmitted data block contains a code word of sufficient length (Barker code) which in the receiving device supplies the requisite block and phase corrections via correlation.
In the case of a mobile radio network as already described in earlier applications of the assignee, a correlation receiver of this type having an extended range of functions is to be used. This mobile radio network represents a synchronous network in which the data traffic and speech traffic between the mobile radio subscriber stations and the stationary, fixed stations is handled with fixed ratio range assignment. Before a conversation is established, organizational data exchange between a mobile subscriber and a fixed station is necessary, such as for example application, rebooking or transfer of dialed number. A separate radio channel (organization channel) is provided for handling purposes in which a plurality of fixed stations can operate with multiple access, therefore with fixed time location assignment. This assignment provides a mobile subscriber with the possibility of entering into an organizational data link with the radio range most favorable for the same via the reception quality control. However, following this establishment in all time slots (radio ranges) the reception quality and the setting-up criteria continued to be measured in order that, in the event of a change in the radio field parameters resulting from a change of location of the mobile subscriber, the new optimum radio range may be immediately recognized and the requisite setting-up information may be ready. If the system properties are fulfilled in this manner, a rebooking process can be fulfilled without problems. The function of the correlation receiver is, on the one hand, to implement the bit and block synchronization for the favorable radio range from an asynchronous state (direct access to the setting-up elements), and, on the other hand, in the event of synchronous operation, to supply the setting-up criteria for the current radio range and, in the event of rebooking, to supply those of all the other possible radio ranges (indirect access to the setting-up elements via a computer).